In a pressurized mechanical refrigeration system, such as an automotive air conditioning system having a compressor, condenser and evaporator, it is necessary to provide valve assemblies for charging the system with refrigerant fluid following installation of the system at an automotive vehicle assembly or repair facility. Such valve assemblies used in prior art systems often have intricate, multiple-piece elements, such as a valve stem, that inherently are costly to manufacture or that have limitations with respect to durability.
It is desirable in high production volume assembly plants to eliminate as much as possible the need for threads in the valve assembly in order to simplify machining, which reduces assembly costs and piece cost. Cost of prior art valve assemblies could be reduced further if the need for using an intricately machined one-piece valve stem or a multiple-piece valve stem could be eliminated. It is important also in the design of such systems to provide a charge flow passage that is capable of high fluid flow in order to reduce evacuation and/or fill time.
Typically, charge valves for use in pressurized mechanical refrigerant systems for automotive vehicles have a valve stem that is formed in two parts--a base part that can be secured to the system housing, and a companion part that is threadably secured to the base part. The companion part of the stem can be one of either two types. The first type uses an independent valve core which threads into the base part. The second type contains a flow valve mechanism that can be retained within the valve stem mechanically. The companion valve stem is then threaded to the base part, thus forming a complete valve stem assembly. The valve stem also can be threaded, either internally or externally, to receive a cap that protects the valve following the filling of the refrigerant system. The cartridge valve and the valve stem with which it registers must be carefully machined to maintain concentricity and close dimensional tolerances. Any additional machining requirement to add threads will further increase the cost of the valve assembly and increase assembly time. It also is necessary to carefully control the magnitude of the torque applied to threaded elements of the assembly in order to protect the system's integrity.
U.S. Pat. No. 5,205,531 discloses an example of a prior art valve design for use with a solenoid actuator. That design includes a unitary valve stem that can be received threadably in a housing, such as an automotive transmission housing. The unitary stem receives a movable poppet valve 32 which seats on an internal valve seat machined in housing port end 22. Movable plunger 52 is slidably received in the valve stem. A plug or stop 60 is threadably received in the open end of the valve stem. This construction, as in the case of other prior art designs, requires careful machining to maintain concentricity between the critical dimensions required by the popper valve and the plunger and to maintain concentricity and alignment of the counterbore 44 in the poppet valve with respect to the counterbore 24 in the base of the valve stem.